Amine mediated proton transfer reaction and C-Cl bond activation of solvent chloroform by a trinuclear copper(II) complex of a glucopyranosylamine derived ligand

An amine mediated C-Cl bond activation process of the solvent chloroform has been explored by a coordinatively labile trinuclear Cu(II) complex, [Cu3(L1)2(MeOH)(H2O)] (1), derived from N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene--D-glucopyranosylamine (H3L1). The effect of activation is extremely high with methylamine, resulting in the formation of [Cu(MeNH2)5]Cl2 (2) and [Cu(L2)2] (3; HL2 = 2-tert-butyl-6-[(methylimino)methyl]phenol), however, under identical conditions it is moderate with ethylamine resulting in the isolation of crystals of the intermediate amine bound trinuclear copper(II) complex, [Cu3(L1)2(EtNH2)2(MeOH)2] (5), which was further converted into the mononuclear complex, [Cu(HL1)(EtNH2)] (6), in a novel crystal-to-crystal transformation. The successive isolation of the ethylamine-bound tri- and mononuclear complexes, 5 and 6, supported the occurrence of proton transfer reactions, which might be a key step in C-Cl bond activation. The primary and secondary amines, 2-aminomethylpyridine, N,N-dimethylethylenediamine, and 1,4,7-triazacyclononane, also having chelating features further enhance the rate of activation. No activation has been noted in the case of triethylamine and N,N,N,N-tetramethylethylenediamine. Formation of a carbene-trapped compound, 2,6-xylyl isocyanide, was confirmed in the reaction of complex 1 with 1,4,7-triazacyclononane and 2,6-xylidine in CHCl3, suggesting that the C-Cl bond cleavage led to the generation of dichlorocarbene. In addition, the mononuclear complex 6 has been transformed into a homotrinuclear complex [Cu3(L1)2(MeOH)2] by treatment with Cu(II) ions in MeOH/CHCl3, suggesting the possibility that the former could be regarded as a suitable metalloligand for heterotrimetallic complex synthesis.     

Four copper(II) pyrazolido complexes derived from reactions of 3{5}-substituted pyrazoles with CuF(2) or Cu(OH)(2)

Treatment of CuF(2) with 2 equiv of 3{5}-[pyrid-2-yl]pyrazole (Hpz(Py)), 3{5}-phenylpyrazole (Hpz(Ph)) or 3{5}-[4-fluorophenyl]pyrazole (Hpz(PhF)) in MeOH, followed by evaporation to dryness and recrystallisation of the solid residues, allows solvated crystals of [{Cu(micro-pz(Py))(pz(Py))}(2)] (1), [{Cu(micro-pz(Ph))(2)}(4)] (2) and [Cu(4)F(2)(micro(4)-F)(micro-pz(PhF))(5)(Hpz(PhF))(4)] (3) to be isolated in moderate-to-good yields. Similar reactions of these three pyrazoles with Cu(OH)(2) in refluxing MeOH respectively afford 1, 2 and [Cu(pz(PhF))(2)(Hpz(PhF))(2)] (4) in ca. 10% yield. Crystalline 1 x 1/2H(2)O x 2CHCl(3) contains two independent dinuclear molecules with a puckered di-(1,2-pyrazolido) bridge motif, linked by a bridging, hydrogen-bonding water molecule. Compound 2 x 1/2C(5)H(12), containing cyclic, square tetranuclear complex molecules, is the first homoleptic divalent metal pyrazolide to have a discrete molecular rather than polymeric structure, for a metal other than Pd or Pt. The two independent complex molecules in 3 x 3/4CH(2)Cl(2) x Hpz(PhF) contain a unique tetrahedral [Cu(4)(micro(4)-F)](7+) core, three of whose edges are spanned by bridging pyrazolido groups. Magnetic data show that the copper centres in 1 and 3 are antiferromagnetically coupled, but that dried bulk samples of 2 do not retain their molecular structure.     

Ferromagnetism in dinuclear copper(II)-phenolate complexes with exogenous O-donor bridges: a comparative study

The copper(II) complex Cu2L(OAc)(H2O)3.5, 1 x 3.5H2O was obtained and its reactivity in a basic medium investigated. Complex 1 x 3.5H2O shows different reaction patterns in air and in an inert atmosphere. Accordingly, interaction of 1 x 3.5H2O with Me4NOH x 5H2O in methanol-acetonitrile in air yields the hydroxide complex Cu2L(OH)(H2O)1.125, 2 x 1.125H2O while Cu2L(OMe)(MeOH)0.5(H2O), 3 x 0.5MeOH x H2O is isolated under an argon atmosphere. The products 1-3 were fully characterised and single crystals of {[Cu2L(OAc)] x MeCN x 3.5H2O}2, 1 x MeCN x 3.5H2O, {[Cu2L(OH)] x MeCN x 1.125H2O}2, 2 x MeCN x 1.125H2O and [Cu2L(OMe)] x 0.5MeOH x H2O, 3 x 0.5MeOH x H2O solved. The single X-ray study shows that 1-3 are dinuclear complexes with an endogenous phenol oxygen and an exogenous O-bridge. Magnetic characterisation of the three dinuclear complexes was performed, showing an apparent anomalous intramolecular ferromagnetic coupling between the metal atoms in all cases.     

Unexpected ferromagnetic interaction in a new tetranuclear copper(II) complex: synthesis, crystal structure, magnetic properties, and theoretical studies

The new tetranuclear carbonate complex [Cu2L)2(CO3)] x 8H2O (1 x 8H2O) (H3L = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) has been obtained by two different synthetic routes and fully characterized. Recrystallization of 1 x 8H2O in methanol yields single crystals of {[(Cu2L)2(CO3)]}2 x 12H2O (1 x 6H2O), suitable for X-ray diffraction studies. The crystal structure of 1 x 6H2O shows two crystallographically different tetranuclear molecules in the asymmetric unit, 1a and 1b. Both molecules can be understood as self-assembled from two dinuclear [Cu2L]+ cations, joined by a mu4-eta(2):eta(1):eta(1) carbonate ligand. The copper atoms of each crystallographically different [(Cu2L)2(CO3)] molecule present miscellaneous coordination polyhedra: in both 1a and 1b, two metal centers are in square pyramidal environments, one displays a square planar chromophore and the other one has a geometry that can be considered as an intermediate between square pyramid and trigonal bipyramid. Magnetic studies reveal net intramolecular ferromagnetic coupling between the metal atoms. Density functional calculations allow the assignment of the different magnetic coupling constants and explain the unexpected ferromagnetic behavior, because of the presence of an unusual NCN bridging moiety and countercomplementarity of the phenoxo (or carbonate) and NCN bridges.     

Cluster-based copper(II) coordination polymers with azido bridges and chiral magnets

Three homochiral layered complexes, [Cu3(R-chea)2(N3)6]n (1), [Cu3(S-chea)2(N3)6]n (2) (chea = 1-cyclohexylethylamine) and [Cu3(S-phpa)2(N3)6]n (3) (phpa = 1-phenylpropylamine), and three novel cluster-based coordination polymers, [Cu6(1,2-pn)4(N3)12]n (4) (1,2-pn = 1,2-diaminopropane), [[Cu8(en)4(N3)16] x H2O]n (5) (en = ethylenediamine) and [Cu6(N-Ipren)2(N3)12]n (6) (N-Ipren = N-isopropylethylenediamine), have been synthesized by the self-assembly reactions of Cu(NO3)2 x 3H2O, NaN3 and small organic amine ligands. Their crystal structures are determined by single-crystal X-ray diffraction. Complexes are composed of neutral 2D brick wall networks with only end-on azido bridges. Complexes and are 3D coordination polymers featuring copper-azido clusters and [Cu(diamine)2]2+ units which are linked by the azido bridges. Complex is a 3D coordination framework based on the hexanuclear copper(II) clusters [Cu6(N3)12(N-Ipren)2]. Magnetic studies show that complexes are interesting chiral ferromagnets with the magnetic transition temperature at ca. 5.0 K. Complexes and show ferromagnetic coupling in the copper-azido cluster units and antiferromagnetic interaction between neighboring units, while complex shows ferromagnetic ordering at 3.2 K.     

Reactions of a tungsten trisulfido complex of hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) [Et(4)N][Tp*WS(3)] with CuX (X = Cl, NCS, or CN): isolation, structures, and third-order NLO properties

Reactions of a tungsten trisulfido complex of hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) [Et4N][Tp*WS3] (1) with 3 equiv of CuCl in CHCl3 afforded a tetranuclear anionic cluster [Et4N][Tp*W(mu3-S)3(CuCl)3] (2), while that of 1 with 3 equiv of CuNCS in MeCN produced a decanuclear neutral cluster (major product) [Tp*W(mu3-S)3Cu3(mu-NCS)3(CuMeCN)]2 (3) along with a binuclear anionic cluster (minor product) [Et4N][Tp*WO(mu-S)2(CuNCS)] (4). Solvothermal reactions of 1 with 3 equiv of CuCN in MeCN at 80 degrees C for 48 h followed by slowly cooling it to ambient temperature gave rise to a polymeric cluster [Tp*W(mu3-S)(mu-S)2Cu2(MeCN)(mu-CN)]n (5). Compounds 2-5 were characterized by elemental analysis, IR, UV-vis, 1H NMR, and single-crystal X-ray crystallography. The cluster anion of 2 has a [Tp*WS3Cu3] incomplete cube with one Cl atom coordinated at each Cu center. 3 is composed of an unprecedented centrosymmetric W2Cu8 cluster core in which each void of the two single incomplete cubane-like [Tp*W(mu3-S)3Cu3(mu-NCS)]+ cations is partially filled with an extra [Cu(MeCN)(mu-NCS)2]- anion via a pair of Cu-mu-NCS-Cu bridges. The cluster anion of 4 contains one WS2Cu core that is formed by an oxidized [Tp*WO(mu-S)2] species and one CuNCS fragment. 5 consists of butterfly shaped [Tp*W(mu3-S)(mu-S)2Cu2(MeCN)] fragments that are interconnected via cyanide bridges to form a 1D spiral chain extending along the c axis. The successful synthesis of 2-5 from 1 suggests that 1 may be an excellent synthon to the W/Cu/S clusters. In addition, the third-order nonlinear optical (NLO) properties of 1-3 in solution were also investigated by femtosecond degenerate four-wave mixing (DFWM) technique with a 80 fs pulse width at 800 nm. Although 2 was not detected to have NLO effects, 1 and 3 exhibited relatively good optical nonlinearities with the nonlinear refractive index n2 and the third-order nonlinear optical susceptibility chi(3) values being 0.79 x 10(-13) and 0.38 x 10(-14) esu (1) and 2.08 x 10(-13) and 1.00 x 10(-14) esu (3), respectively. The second-order hyperpolarizability gamma value for 3 (5.46 x 10(-32) esu) is ca. 5 times larger than that of its precursor 1.     

Synthesis, characterization, and structures of copper(II)-thiosulfate complexes incorporating tripodal tetraamine ligands

The reaction of [Cu(L)(H(2)O)](2+) with an excess of thiosulfate in aqueous solution produces a blue to green color change indicative of thiosulfate coordination to Cu(II) [L = tren, Bz(3)tren, Me(6)tren, and Me(3)tren; tren = tris(2-aminoethyl)amine, Bz(3)tren = tris(2-benzylaminoethyl)amine, Me(6)tren = tris(2,2-dimethylaminoethyl)amine, and Me(3)tren = tris(2-methylaminoethyl)amine]. In excess thiosulfate, only [Cu(Me(6)tren)(H(2)O)](2+) promotes the oxidation of thiosulfate to polythionates. Products suitable for single-crystal X-ray diffraction analyses were obtained for three thiosulfate complexes, namely, [Cu(tren)(S(2)O(3))].H(2)O, [Cu(Bz(3)tren)(S(2)O(3))].MeOH, and (H(3)Me(3)tren)[Cu(Me(3)tren)(S(2)O(3))](2)(ClO(4))(3). Isolation of [Cu(Me(6)tren)(S(2)O(3))] was prevented by its reactivity. In each complex, the copper(II) center is found in a trigonal bipyramidal (TBP) geometry consisting of four amine nitrogen atoms, with the bridgehead nitrogen in an axial position and an S-bound thiosulfate in the other axial site. Each structure exhibits H bonding (involving the amine ligand, thiosulfate, and solvent molecule, if present), forming either 2D sheets or 1D chains. The structure of [Cu(Me(3)tren)(MeCN)](ClO(4))(2) was also determined for comparison since no structures of mononuclear Cu(II)-Me(3)tren complexes have been reported. The thiosulfate binding constant was determined spectrophotometrically for each Cu(II)-amine complex. Three complexes yielded the highest values reported to date [K(f) = (1.82 +/- 0.09) x 10(3) M(-1) for tren, (4.30 +/- 0.21) x 10(4) M(-1) for Bz(3)tren, and (2.13 +/- 0.05) x 10(3) M(-1) for Me(3)tren], while for Me(6)tren, the binding constant was much smaller (40 +/- 10 M(-1)).     

Reversible dioxygen binding and phenol oxygenation in a tyrosinase model system

The complex [Cu2(L-66)]2+ (L-66 = a,a'-bis?bis[2-(1'-methyl-2'-benzimidazolyl)ethyl]amino?-m-xylene) undergoes fully reversible oxygenation at low temperature in acetone. The optical [lambda(max) = 362 (epsilon 15000), 455 (epsilon 2000), and 550 nm (epsilon 900M(-1)cm(-1))] and resonance Raman features (760 cm(-1), shifted to 719cm(-1)(-1) with 18O2) of the dioxygen adduct [Cu2(L-66)(O2)]2+ indicate that it is a mu-eta2:eta2-peroxodicopper(II) complex. The kinetics of dioxygen binding, studied at - 78 degrees C, gave the rate constant k1 = 1.1M(-1) 5(-1) for adduct formation, and k(-1) =7.8 x 10(-5)s(-1), for dioxygen release from the Cu2O2 complex. From these values, the O2 binding constant K= 1.4 x 10(4)M(-1) at -78 degrees C could be determined. The [Cu2(L-66)(O2)]2+ complex performs the regiospecific ortho-hydroxylation of 4-carbomethoxyphenolate to the corresponding catecholate and the oxidation of 3,5-di-tert-butylcatechol to the quinone at -60 degrees C. Therefore, [Cu2(L-66)]2+ is the first synthetic complex to form a stable dioxygen adduct and exhibit true tyrosinase-like activity on exogenous phenolic compounds.     

Copper(II) mediated anion dependent formation of Schiff base complexes

A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.     

Synthesis, structures, and magnetic properties of tri- and dinuclear copper(II)-gadolinium(III) complexes of linear oligooxime ligands

We have designed and synthesized a new Cu2Gd heterotrinuclear complex, [LCu2Gd(OAc)3] (1), where H4L is a bis(salen)-type tetraoxime ligand useful in the synthesis of discrete (3d)2(4f) complexes. Complex 1 crystallizes in the triclinic system, space group P1, with unit cell parameters a = 12.442(4) A, b = 13.397(3) A, c = 13.966(4) A, alpha = 77.052(8) degrees, beta = 88.656(10) degrees, gamma = 77.761(8) degrees, and Z = 2. In the crystal structure of 1, Cu-Gd distances are 3.3-3.5 A, whereas the two Cu atoms are separated by 6.08 A. The corresponding dinuclear CuGd complexes, 2 and 3, with mono(salen)-type chelate 3-MeOsalamo were also synthesized. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c, with unit cell parameters a = 13.869(8) A, b = 13.688(7) A, c = 18.728(10) A, beta = 92.861(8) degrees, and Z = 4, and complex 3 crystallizes in the triclinic system, space group P1, with unit cell parameters a = 12.319(4) A, b = 13.989(4) A, c = 16.774(5) A, alpha = 64.699(14) degrees, beta = 66.672(13) degrees, gamma = 76.891(17) degrees, and Z = 4. Interaction between Cu(II) and Gd(III) in the dinuclear complexes 2 and 3 is ferromagnetic (J = 4.5 and 7.6 cm(-1), respectively, using spin Hamiltonian H = -JS(Cu) x S(Gd)) as observed in the previously prepared [LCuGdX3] complexes, where L is a salen-type chelate. Magnetic data for the Cu2Gd trinuclear complex can be reasonably interpreted with the use of a spin Hamiltonian H = -J(CuGd)S(Cu1) x S(Gd) - J(CuGd)S(Cu2) x S(Gd) - J(CuCu)S(Cu1) x S(Cu2) with J(CuGd) = 5.0 cm(-1) and J(CuCu) = 0 cm(-1). The S = 9/2 ground state resulted from the ferromagnetic interaction among the Cu(II)-Gd(III)-Cu(II) triad was also supported by the saturation magnetization at 1.8 K.     

Structural characterization and formation kinetics of sitting-atop (SAT) complexes of some porphyrins with copper(II) ion in aqueous acetonitrile relevant to porphyrin metalation mechanism. Structures of aquacopper(II) and cu(II)-SAT complexes as determined by XAFS spectroscopy

The formation of the sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin (H(2)tpp), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (H(2)t(4-Clp)p), 5,10,15,20-tetramesitylporphyrin (H(2)tmp), and 2,3,7,8,12,13,17,18-octaethylporphyrin (H(2)oep) with the Cu(II) ion was spectrophotometrically confirmed in aqueous acetonitrile (AN), and the formation rates were determined as a function of the water concentration (C(W)). The decrease in the conditional first-order rate constants with the increasing C(W) was reproduced by taking into consideration the contribution of [Cu(H(2)O)(an)(5)](2+) in addition to [Cu(an)(6)](2+) to form the Cu(II)-SAT complexes. The second-order rate constants for the reaction of [Cu(an)(6)](2+) and [Cu(H(2)O)(an)(5)](2+) at 298 K were respectively determined as follows: (4.1 +/- 0.2) x 10(5) and (3.6 +/- 0.2) x 10(4) M(-1) s(-1) for H(2)tpp, (1.15 +/- 0.06) x 10(5) M(-1) s(-1) and negligible for H(2)t(4-Clp)p, and (4.8 +/- 0.3) x 10(3) and (1.3 +/- 0.3) x 10(2) M(-1) s(-1) for H(2)tmp. Since the reaction of H(2)oep was too fast to observe the reaction trace due to the dead time of 2 ms for the present stopped-flow technique, the rate constant was estimated to be greater than 1.5 x 10(6) M(-1) s(-1). According to the structure of the Cu(II)-SAT complexes determined by the fluorescent XAFS measurements, two pyrrolenine nitrogens of the meso-substituted porphyrins (H(2)tpp and H(2)tmp) bind to the Cu(II) ion with a Cu-N(pyr) distance of ca. 2.04 A, while those of the beta-pyrrole-substituted porphyrin (H(2)oep) coordinate with the corresponding bond distance of 1.97 A. The shorter distance of H(2)oep is ascribed to the flexibility of the porphyrin ring, and the much greater rate for the formation of the Cu(II)-SAT complex of H(2)oep than those for the meso-substituted porphyrins is interpreted as due to a small energetic loss at the porphyrin deformation step during the formation of the Cu(II)-SAT complex. The overall formation constants, beta(n), of [Cu(H(2)O)(n)()(an)(6)(-)(n)](2+) for the water addition in aqueous AN were spectrophotometrically determined at 298 K as follows: log(beta(1)/M(-1)) = 1.19 +/- 0.18, log(beta(2)/M(-2)) = 1.86 +/- 0.35, and log(beta(3)/M(-3)) = 2.12 +/- 0.57. The structure parameters around the Cu(II) ion in [Cu(H(2)O)(n)(an)(6-n)](2+) were determined using XAFS spectroscopy.     

Electron delocalisation in a trinuclear copper(II) complex: high-field EPR characterization and magnetic properties of Na3[Cu3(mal)3(H2O)] x 8H2O

The complex Na3[Cu3(mal)3(H2O)] x 8H2O was obtained from evaporation of an aqueous solution containing Cu(OAc)2, malic acid (HO2CCH2CHOHCO2H) and NaOH and was characterised by X-ray diffraction on single crystal, X-band and high-field EPR spectroscopy (HF-EPR) and magnetic susceptibility measurements. The trinuclear complex [Cu3(mal)3(H2O)]3- is trapped in a three-dimensional network with sodium cations. The three copper atoms are connected by alkoxo bridges and form an almost isosceles triangle with Cu...Cu distances of 3.076(1), 3.504(1) and 3.513(1) A. Two of the copper ions are also bridged by an extra aquo ligand. EPR spectroscopy combined with magnetic susceptibility measurements provide a powerful tool to resolve the electronic structure of the complex. The overall magnetic behaviour corresponds to an antiferromagnetically coupled triangular system. The 285 GHz-EPR spectrum (g = 2; 10.18 T) is characteristic of a spin state S = 1/2, with a rhombic anisotropy of [g]. This rhombic pattern allows us to propose that the electronic spin density is delocalised on the three copper ions.     

Self-assembly and interconversion of tetranuclear copper(II) complexes

The ligand 1,2-bis(benzimidazol-2-yl)-1,2-ethanediol (H2bzimed, 1) and its N-methylated analogue (H2mbzimed, 2) form a variety of polynuclear complexes with copper(II), all of which contain a planar Cu2O2 lozenge as a central element and in which the bridging oxygen belongs to an alkoxo group of the ligand. Syntheses are reported for dinuclear [Cu2(Hmbzimed)2](ClO4)2 x 1.5H2O, Cu(2)2(2), and the tetranuclear species [Cu4(Hbzimed)4(ClO4)2](NO3)2 x 4H2O, Cu(4)1(4), [Cu4(Hmbzimed)2(mbzimed)Cl2](ClO4)2 x 2H2O x C2H5OH, Cu(4)2(3), and rac-[Cu4(H2bzimed)4(bzimed)(ClO4)2](ClO4)4 x 1.5H2O x 3.5C2H5OH, Cu(4)1(5). Crystal structures are reported for the tetranuclear species. Cu(4)1(4) shows a cubane structure, Cu(4)2(3) a stepped cubane structure, and rac-Cu(4)1(5) a novel structure in which one doubly deprotonated ligand lies between the two Cu2O2 units. Magnetic susceptibility measurements indicate that all complexes show antiferromagnetic coupling in the solid state. Studies in solution (ESI-MS, CD, NMR) show that Cu(2)2(2) and Cu(4)2(3) persist in solution but that Cu(4)1(4) dissociates partially and rac-Cu(4)1(5) completely. The six coordination modes of the ligands are discussed together with the effect of the N-methylation on the ligand conformation.     

Intra and intermolecular magnetic interactions in a series of dinuclear Cu(II)/hxta complexes [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: correlation of magnetic properties with geometry

Nine dinuclear copper(II) complexes with hxta5- ligands [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: [Cu2(MeO-hxtaH)(H2O)2] x 4H2O (1), [Na(micro-H2O)2(H2O)6][Cu2(Cl-hxta)(H2O)3]2 x 6H2O (2), [Cu(H2O)6][Cu2(Me-hxta)(H2O)2](NO3) x 2H2O (3), [Cu2(R-hxtaH)(H2O)3] x 3H2O [R = Cl (4), CH3 (5), and MeO (6)], [Cu2(MeO-hxtaH2)(micro-X)(CH3OH)] x 3CH3OH [X = Cl (7), Br (8)] and K5Na(micro-H2O)10[Cu2(micro-CO3)(Me-hxta)]2 x 4H2O (9), have been synthesized and structurally characterized. In complexes 4-7, the dinuclear units are linked via novel pairwise supramolecular interactions involving the ligand carboxylate groups. The intra- and intermolecular magnetic interactions have been quantified, and the coupling constants have been related to the structural geometries.     

Isotropic and antisymmetric double-exchange, zero-field, Zeeman, and hyperfine splittings in trinuclear valence-delocalized [Cu3(7+)] clusters

Valence delocalization in the [Cu3(7+)] trimer is considered in the model of the double-exchange coupling, in which full delocalization corresponds to the migration of the single d(x2-y2) hole and relatively strong isotropic double-exchange coupling. Strong double exchange results in the pairing of the individual spins in the delocalized trimer even at room temperature. The model explains the delocalized singlet 1A1 ground state in the planar Cu3(mu3-O) core by strong double exchange with positive double-exchange parameter t(0), whereas the delocalized triplet ground state of the [Cu3(7+)] trimer, which was observed in the Cu3(mu3-S)2 cluster, may be explained by the double exchange with relatively weak positive t(0): 0 < t(0) < 2J (degenerate 3E ground state) or negative t(0) (triplet 3A2 ground state). An analysis of the splitting of the delocalized degenerate 3E term requires inclusion of the antisymmetric double-exchange interaction, which takes into account the spin-orbit coupling in the double-exchange model. The cluster parameter KZ of the antisymmetric double-exchange coupling is proportional to t(0) and anisotropy of the g factor Deltag(parallel)[Cu(II)], KZ < t(0). Antisymmetric double exchange is relatively large in the [Cu3(7+)] cluster with the d(x2-y2) magnetic orbitals lying in the Cu3 plane [Cu3(mu3-O) core], whereas for the d(x2-y2) magnetic orbitals lying in the plane perpendicular to Cu3, antisymmetric double-exchange coupling is weak [Cu3(mu3-S)2 cluster]. The antisymmetric double-exchange coupling results in the linear zero-field splitting DeltaK = 2[equation: see text]KZ (approximately t(0)) of the delocalized degenerate 3E term that leads to strong anisotropy of the Zeeman splittings in the external magnetic field and a complex electron paramagnetic resonance (EPR) spectrum. The delocalized model of hyperfine interaction explains the hyperfine structure [10 hyperfine lines with the relative intensities 1:3:6:10:12:12:10:6:3:1 and the interval a/3] of the EPR transitions in the triplet states that was observed in the EPR spectra of the Cu3(mu3-S)2 cluster.     

Self-assembly of polyoxometalate-based metal organic frameworks based on octamolybdates and copper-organic units: from Cu(II), Cu(I,II) to Cu(I) via changing organic amine

Six polyoxometalate (POM)-based hybrid materials have been designed and synthesized based on octamolybdate building blocks and copper-organic units at different pH values under hydrothermal conditions, namely, [H2bbi][Cu(II)(bbi)2(beta-Mo8O26)] (1), [Cu(II)(bbi)2(H2O)(beta-Mo8O26)0.5] (2), [Cu(II)(bbi)2(alpha-Mo8O26)][Cu(I)(bbi)]2 (3), [Cu(II)Cu(I)(bbi)3(alpha-Mo8O26)][Cu(I)(bbi)] (4), [Cu(I)(bbi)]2[Cu(I)2(bbi)2(delta-Mo8O26)0.5][alpha-Mo8O26]0.5 (5), and [Cu(I)(bbi)][Cu(I)(bbi)(theta-Mo8O26)0.5] (6), where bbi is 1,1'-(1,4-butanediyl)bis(imidazole). Their crystal structures have been determined by X-ray diffraction. In compound 1, the bbi ligands with bis-monodentate coordination modes link Cu(II) cations to generate a 2D copper-organic unit with (4, 4) net, which is pillared by the (beta-Mo8O26)(4-) anions to form a 3D framework with alpha-Po topology. The similar copper-organic units are connected alternately by (beta-Mo8O26)(4-) anions to generate a 3D 2-fold interpenetrating (4,6)-connected framework with (4(4) x 6(2))(4(4) x 6(10) x 8) topology in compound 2. Compounds 3 and 4 are supramolecular isomers with polythreaded topology. If Cu (I)...O interactions are considered, the structure of 3 is a novel self-penetrating (3,4,6)-connected framework with (5(2) x 8)2(5(4) x 6 x 8)(4(4) x 6(10) x 10) topology, and the structure of 4 is a (4,6)-connected framework with (4(2) x 6(3) x 7)(5.6(4) x 8)(4(2) x 5(6) x 6(6) x 8)(4(2) x 5(6) x 6(4) x 7 x 8(2)) topology. Different from compounds 3 and 4, compounds 5 and 6 are supramolecular isomers with polythreaded topology based on different octamolybdate isomers. By careful inspection of the structures of 1-6, it is believed that various copper-organic units, which are formed by bbi ligands combined with Cu(II)/Cu(I) cations, octamolybdates with different types and coordination modes, and the nonbonding interactions between polyanions and copper-organic units are important for the formation of the different structures. In addition, with step by step increasing of the amount of organic amine, we have achieved the transformation of Cu(II) ions into Cu(I) ones in different degrees in POMs-based metal-organic frameworks (MOFs) for the first time. The infrared spectra, X-ray powder diffraction, and thermogravimetric analyses have been investigated in detail for all compounds, and the luminescent properties have been also been investigated for compounds 3 and 4.     

Effects of auxiliary complex-forming agents on the rate of metallochromic indicator colour change-IV Mechanism of the colour change of xylenol orange in copper(II)-edta titrations

The rate of ligand substitution of copper(II)-Xylenol Orange (XO) with EDTA (Y) has been determined spectrophotometrically over the pH range 4.8-6.0 at mu = 0.1 (KNO(3)) and at 25 degrees . In 2-(N-morpholino)ethane sulphonic acid buffer, copper forms a 2:1 chelate (Cu(2)XO(2-)) with XO, and the rate-law is expressed as -d[Cu(2)XO(2-)]/dt = 10(2.89)[Cu(2)XO(2)-][Y']- The release of the first copper ion from Cu(2)XO(2-) is the rate-determining step. The resulting CuHXO(3-) or CuH(2)XO(2-) may undergo fast substitution with EDTA. In the presence of hexamine, the copper(II)-XO chelate forms a mixed-ligand complex with hexamine (L). The formation constant K(Cu(2)XOL)(L) = [Cu(2)XOL(2-)]/[Cu(2)XO(2-)] [L] = 10(2.14) (mu = 0.1, 25 degrees ). At 3 x 10(-2)-2 x 10(-1)M hexamine the rate-law is expressed as -d[Cu(2)XOL(2-)]/dt = 5.39[Cu(2)XOL(2-)][Y']/[L']. The dissociation of hexamine from Cu(23)XOL(2-) has to precede the substitution reaction of Cu(2)XO(2-) with EDTA. Hence, hexamine at higher concentrations than 10(-3)M slows down the rate of colour change of XO in the copper-EDTA titration.     

Octanuclear and nonanuclear supramolecular copper(II) complexes with linear "tritopic" ligands: structural and magnetic studies

The structures and magnetic properties of self-assembled copper(II) clusters and grids with the "tritopic" ligands 2poap (a), Cl2poap (b), m2poap (c), Cl2pomp (d), and 2pomp (e) are described [ligands derived by reaction of 4-R-2,6-pyridinedicarboxylic hydrazide (R = H, Cl, MeO) with 2-pyridinemethylimidate (a-c, respectively) or 2-acetylpyridine (d, R = Cl; e, R = H)]. Cl2poap and Cl2pomp self-assemble with Cu(NO(3))(2) to form octanuclear "pinwheel" cluster complexes [Cu(8)(Cl2poap-2H)(4)(NO(3))(8)].20H(2)O (1) and [Cu(8)(Cl2pomp-2H)(4)(NO(3))(8)].15H(2)O (2), built on a square [2 x 2] grid with four pendant copper arms, using "mild" reaction conditions. Similar reactions of Cl2pomp and 2pomp with Cu(ClO(4))(2) produce pinwheel clusters [Cu(8)(Cl2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8).7H(2)O (3) and [Cu(8)(2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8) (4), respectively. Heating a solution of 1 in MeOH/H(2)O produces a [3 x 3] nonanuclear square grid complex, [Cu(9)(Cl2poap-H)(3)(Cl2poap-2H)(3)](NO(3))(9).18H(2)O (5), which is also produced by direct reaction of the ligand and metal salt under similar conditions. Reaction of m2poap with Cu(NO(3))(2) produces only the [3 x 3] grid [Cu(9)(m2poap-H)(2)(m2poap-2H)(4)](NO(3))(8).17H(2)O (6) under similar conditions. Mixing the tritopic ligand 2poap with pyridine-2,6-dicarboxylic acid (picd) in the presence of Cu(NO(3))(2) produces a remarkable mixed ligand, nonanuclear grid complex [Cu(9)(2poap-H)(4)(picd-H)(3)(picd-2H)](NO(3))(9).9H(2)O (7), in which aromatic pi-stacking interactions are important in stabilizing the structure. Complexes 1-3 and 5-7 involve single oxygen atom (alkoxide) bridging connections between adjacent copper centers, while complex 4 has an unprecedented mixed micro-(N-N) and micro-O metal ion connectivity. Compound 1 (C(76)H(92)N(44)Cu(8)O(50)Cl(4)) crystallizes in the tetragonal system, space group I, with a = 21.645(1) A, c = 12.950(1) A, and Z = 2. Compound 2 (C(84)H(88)N(36)O(44)Cl(4)Cu(8)) crystallizes in the tetragonal system, space group I, with a = 21.2562(8) A, c = 12.7583(9) A, and Z = 2. Compound 4 (C(84)H(120)N(28)O(66)Cl(8)Cu(8)) crystallizes in the tetragonal system, space group I4(1)/a, with a = 20.7790(4) A, c = 32.561(1) A, and Z = 4. Compound 7(C(104)H(104)N(46)O(56)Cu(9)) crystallizes in the triclinic system, space group P, with a = 15.473(1) A, b = 19.869(2) A, c = 23.083(2) A, alpha = 88.890(2) degrees, beta = 81.511(2) degrees, gamma = 68.607(1) degrees, and Z = 2. All complexes exhibit dominant intramolecular ferromagnetic exchange coupling, resulting from an orthogonal bridging arrangement within each polynuclear structure.     

Carboxymethylated cage amines: coordination and lactamization

Depending upon the position and degree of substitution, carboxymethyl derivatives of cage amines of the "sarcophagine" (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) type vary considerably in the stability of their lactamized forms. For 1,8-diamino-3-carboxymethylsarcophagine, L(1), only indirect evidence for some involvement of a lactamized form of its Ni(II) complex has been obtained. Crystal structure determinations for [Cu(H(2)L(1))](NO(3))(3.5)Cl(0.5) x 2.5H(2)O and [Ni(HL(1))]Cl(3) x 3H(2)O show distorted octahedral coordination of all six endocyclic N-donor atoms in both cases. For related diaminosarcophagine derivatives with either two (1,8; L(2)) or three (1,1,8; L(3)) carboxymethyl substituents on the exocyclic N atoms, crystallographic studies have shown a dilactam form for the ligands in their Ni(II) and Cu(II) complexes which is of almost identical conformation to that of the diprotonated "free" ligand in [H(2)L(3)][ZnCl(4)] x 6H(2)O. The lactamized ligands appear to strongly favor square planar four-coordination, and the Co(II) complex of L(2) shows a remarkable lack of reactivity toward oxygen. Kinetic studies indicate that the hydrolytic stability of the lactam rings is comparable to that of uncoordinated analogues.     

Synthesis and structure of [2 x 2] molecular grid copper(II) and nickel(II) complexes with a new polydentate oxime-containing Schiff base ligand

A new polynucleating oxime-containing Schiff base ligand, 2-hydroxyimino- N'-[1-(2-pyridyl)ethylidene]propanohydrazone (H pop), has been synthesized and fully characterized. pH potentiometric, electrospray ionization mass spectrometric, and spectrophotometric studies of complex formation in H 2O/DMSO solution confirmed the preference for polynuclear complexes with 3d metal ions. Single-crystal X-ray diffraction analyses of [Ni 4( pop) 4(HCOO) 4].7H 2O ( 1), [Cu 4( pop-H) 4(HCOOH) 4].H 2O ( 2), and [Cu 4( pop-H) 4(H 2O) 4].9H 2O ( 3) indicated the presence of a [2 x 2] molecular grid structure in all three compounds but distinct configurations of the cores: a head-to-tail ligand arrangement with overall S 4 symmetry of the grid in the Cu (2+) complexes as opposed to a head-to-head ligand arrangement with (noncrystallographic) C 2 grid symmetry for the Ni (2+) complex. A cryomagnetic study of 3 revealed intramolecular ferromagnetic exchange between copper ions in the grid, while in 1, antiferromagnetic interactions between the metal ions were observed.